690 Part IV / Perception
嗅上皮
犁鼻器
外侧嗅束
前嗅核
梨状皮层
嗅结节
杏仁核
内嗅皮层
对侧嗅球
下丘脑
海马体
丘脑
下丘脑
眶额皮层
前额叶皮层
僧帽
细胞
簇状
细胞
嗅球
嗅觉皮层
副嗅球
僧帽
细胞
Figure 29–8 Afferent pathways to olfactory cortex. The axons
of mitral and tufted relay neurons of the olfactory bulb project
through the lateral olfactory tract to the olfactory cortex. The olfac-
tory cortex consists of a number of distinct areas, the largest of
which is the piriform cortex. From these areas, olfactory informa-
tion is transmitted to other brain areas directly as well as indirectly
via the thalamus. Targets include frontal and orbitofrontal areas
of the neocortex, which are thought to be important for odor dis-
crimination, and the amygdala and hypothalamus, which may be
involved in emotional and physiological responses to odors. Mitral
cells in the accessory olfactory bulb project to specific areas of the
amygdala that transmit signals to the hypothalamus.
to form excitatory glutamatergic synapses with pyrami-
dal neurons, the projection neurons of the cortex.
Pyramidal neuron activity appears to be modulated by
inhibitory inputs from local GABAergic interneurons
as well as by excitatory inputs from other pyramidal
neurons in the same and other olfactory cortical areas
and the contralateral piriform cortex. The piriform cor-
tex also receives centrifugal inputs from modulatory
brain areas, suggesting that its activity may be adjusted
according to physiological or behavioral state. Finally,
the olfactory cortex projects to the olfactory bulb, pro-
viding yet another possible means of signal modulation.
As with the olfactory bulb relay neurons, indi-
vidual pyramidal neurons can be activated by more
than one odorant. However, the pyramidal neurons
activated by a particular odorant are scattered across
the piriform cortex, an arrangement different from that
of the olfactory bulb. Mitral cells in different parts of
the olfactory bulb can project axons to the same sub-
region of the piriform cortex, further indicating that
the highly organized map of odorant receptor inputs
in the olfactory bulb is not recapitulated in the cortex.
Output From the Olfactory Cortex Reaches Higher
Cortical and Limbic Areas
Pyramidal neurons in the olfactory cortex transmit
information indirectly to the orbitofrontal cortex
through the thalamus and directly to the frontal cortex.
These pathways to higher cortical areas are thought to
be important in odor discrimination. In fact, people
with lesions of the orbitofrontal cortex are unable to
discriminate odors. Interestingly, recordings in the
orbitofrontal cortex suggest that some individual neu-
rons in that area receive multimodal input, responding,
for example, to the smell, sight, or taste of a banana.
Many areas of the olfactory cortex also relay
information to nonolfactory areas of the amygdala,
which is linked to emotions, and to the hypothala-
mus, which controls basic drives, such as appetite, as
well as a number of innate behaviors. These limbic
areas are thought to play a role in the emotional and
motivational aspects of smell as well as many of the
behavioral and physiological effects of odorants. In
animals, they may be important in the generation of
Kandel-Ch29_0682-0706.indd 690 12/12/20 3:20 PM